In some mobile communications networks, mobile subscribers prepay a network operator for SMS message service. For example, some mobile subscribers may prepay for the right to send 100 SMS messages in a given month. Other mobile subscribers may not prepay for SMS message service and instead pay after the fact for the amount of SMS messages sent or received within a given month.
Currently, network operators generate intelligent network (IN) queries to an accounting database for SMS messages originating from both prepaid and postpaid mobile subscribers. For prepaid mobile subscribers, the lookup in the database determines whether the mobile subscriber has sufficient credit for sending an SMS message. If the mobile subscriber has sufficient credit, the database returns a response and the SMS message is delivered to its intended recipient. For postpaid mobile subscribers, the lookup in the accounting database is wasteful, since no prepaid SMS information exists in the database for postpaid subscribers. In this case, the database returns a response indicating that the SMS message should be delivered to its intended recipient.
Using IN queries to perform prepaid SMS accounting functions increases network traffic and delays SMS message delivery. For example, the sending MSC must formulate the IN query and suspend delivery of the SMS message until the response arrives. Formulating IN queries to the accounting database for both prepaid and postpaid subscribers further increases network traffic, SMS message delivery time, and the number of hits to the prepaid SMS accounting database.
Another problem with SMS service relates to number portability. When a mobile subscriber changes service providers and decides to keep his or her mobile telephone number, the telephone number is ported from the original network to the new network. However, the originating mobile subscriber may still have access to the SMSC in the original network because networks typically do not screen SMS messages originated by ported subscribers.
One proposed solution to these problems associated with SMS service is to locate a signaling relay function in the network between a mobile switching center and a pre-paid SMS server. FIG. 1 illustrates this solution. In FIG. 1, a signaling relay function (SRF) 100 and a prepaid SMS server 102 are located between a mobile switching center (MSC) 104 and a short message service center 106 in a mobile communications network. In this proposed solution, in step 1, MSC 104 originates a mobile-originated forward short message (MO FSM) message to a signaling relay function 100. SRF 100 identifies the operation code of the MO FSM message and analyses the MSISDN of the calling subscriber. In this case, the subscriber is a prepaid SMS subscriber (with information registered in the SRF database), and SRF 100 relays the MO FSM message to a prepaid SMS server 102 (step 2).
In step 3, prepaid SMS server 102 authorises the calling subscriber to send an SMS message. Prepaid SMS server 102 opens a new TCAP dialog towards SMSC 106 by sending a MO FSM message to SRF 102 with SMSC 106 as final destination.
In step 4, SRF 106 relays the MO FSM message to SMSC 106. In step 5, SMSC 106 acknowledges the MO FSM message by sending a MO FSM Ack message directly to prepaid SMS server 102. In step 6, prepaid SMS server 102 acknowledges the MO FSM message received in the step 2 by sending a FSM MO Ack to SRF 100 with MSC 104 as final destination. In step 7, SRF 100 relays the MO FSM Ack message to MSC 104.
As illustrated in the solution in FIG. 1, locating a signalling relay function and a separate prepaid SMS server in the network results in multiple MAP messages in the network. For example, in FIG. 1, the MAP dialog between SRF and the prepaid SMS server results in three additional MAP messages (the MAP MO FSM messages in steps 2 and 3 and the MAP MO FSM ack message in step 6) for every SMS message sent. In light of the expected increase in SMS traffic in the networks, such additional message traffic is undesirable.
Another problem with prepaid SMS solutions, such as that illustrated in FIG. 1, relates to prepaid roaming. When an SMS subscriber is roaming, SMS messages originated by the subscriber must travel to one of the subscriber's home network SMSCs to be delivered to the intended destination. For IN-based solutions, the MSC in the visited network must query the prepaid SMS accounting database to determine whether the subscriber has sufficient prepaid SMS credit to send the message. The home network must depend on the visited network to make this determination. This is undesirable because it requires the operator of the home network to rely on the visited network for prepaid SMS screening and accounting. Such a solution is not practical because a prepaid SMS service provider would be required to have prepaid SMS accounting agreements with all networks in which any of its subscribers desires to roam. Thus, there exists a need for improved methods and systems for providing screening service for prepaid SMS messages.